Semiconductor device

ABSTRACT

In a semiconductor device that generates a power supply voltage from an RF carrier signal received by an antenna through the use of a rectification circuit, rectification circuits, each including a plurality of capacitors and a plurality of diodes, are connected in multistage. The rectification circuits includes limiter circuits that are turned on at a voltage larger than an on-voltage of the diodes, clamp cathodes of the diodes at a first voltage. The limiter circuits and the diodes are connected in parallel between the capacitors connected to the antenna connection terminal and a node supplied reference potential VSS of the power supply voltage.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2014-170602, filed on Aug. 25,2014, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments discussed herein are directed to a semiconductor device.

BACKGROUND

In recent years, automatic recognition, information management, andtraceability management using radio frequency identification (RFID) havebeen spread. RFID systems are used in various industrial fields becausedata is writable, large amount of information can be processed, and longdistance communication is allowed. Frequencies used in RFID systemsinclude HF band (mainly 13.56 MHz) and UHF band (860 MHz to 960 MHz).RFID systems using UHF band are becoming smaller component and can beused for longer distance communication because the used frequency ishigh (wavelength is short).

An RFID system includes a reader/writer (R/W) and an RFID tag, eachincluding an antenna. The reader/writer modulates radio frequency (RF)carrier signals corresponding a command and transmits the modulated RFcarrier signals. The RFID tag receives signals from the reader/writerand generates a DC power from an RF carrier signal. The RFID tag thendrives a circuit by the generated DC power, interprets the receivedcommand, and performs a process corresponding to the command. When thecommand requests a response, the RFID tag generates binary data byreflecting or absorbing the received RF carrier signal by the modulationcircuit based on the data generated within the RFID tag and responseswith the generated binary data.

In a typical RFID system, the distance between a reader/writer and anRFID tag is not defined, and an RFID system is used at various distancesdepending on customers' use. Thus, one of requirements for an RFID tagis that stable communication is possible regardless the distance betweena reader/writer and the RFID tag, in other words, the dynamic rangethereof is wide. Therefore, an RFID tag is typically designed such thatthe RFID tag can be operated in communication at a long distance. For anRFID tag, thus, a circuit is designed such that receive and responseoperation is possible with a small power, and the circuit can beoperated even with small input amplitude.

In some cases, when an RFID tag is close to a reader/writer, maximumtransmission power in conformance with a regulation and the like atplace of use may be input to an antenna of the RFID tag. Setting thetransmission power of a reader/writer to a certain value varies thereception power of an RFID tag inverse-proportionally with the square ofthe distance between the reader/writer and the RFID tag. This makes thereception power of an RFID tag that is designed to be operable with asmall power very large when the RFID tag is close to a reader/writer.Thus, reception performance of large signals may be unstable or largesignal reception may be difficult, disabling communication in widedynamic range.

In a semiconductor integrated circuit device that is used in an RFID tagand generates a DC power from radio waves received by an antenna, thereis proposed a technique to limit output voltage not to increase beyond acertain voltage by providing a voltage limit circuit causing current toflow toward the reference potential when the output voltage output fromthe output terminal increases beyond the certain voltage (refer toPatent Document 1, for example). In addition, in a device for convertingmagnetic energy to rectified electrical energy, there is proposed atechnique to discharge surplus energy charged in a magnetic fieldconverter circuit through the use of a discharge-promoting circuit(refer to Patent Document 2, for example).

[Patent Document 1] Japanese Laid-open Patent Publication No.2008-236961 [Patent Document 2] Japanese National Publication ofInternational Patent Application No. 2001-516460 SUMMARY

One aspect of a semiconductor device includes: an antenna that transmitsand receives a wireless signal; and a rectification circuit thatincludes unit rectification circuits connected in multistage andgenerates a power supply voltage from the wireless signal received bythe antenna, each unit rectification circuit includes a plurality ofcapacitors and a plurality of diodes. The rectification circuit includeslimiter circuits that are turned on at a voltage larger than anon-voltage of the diodes, clamp cathodes of the diodes at a firstvoltage. Between the capacitors connected to the antenna connectionterminal and a node supplied a reference potential of the power supplyvoltage, the diodes and the limiter circuits are connected in parallel.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram depicting a configuration example of an RFID systemin a present embodiment;

FIG. 2 is a diagram depicting a configuration example of a rectificationcircuit;

FIG. 3 is a diagram depicting a configuration example of a rectificationcircuit by using unit rectification circuits connected in multistage;

FIG. 4 is a diagram depicting an example of a received radio wave;

FIG. 5 is a diagram depicting change over time of potentials ofrespective nodes in the rectification circuit depicted in FIG. 3;

FIG. 6 is a diagram depicting a layout example of diodes in therectification circuits depicted in FIG. 3;

FIG. 7 is a sectional view taken along the line I-I in FIG. 6;

FIG. 8 is a diagram depicting a configuration example of a rectificationcircuit in the present embodiment;

FIG. 9 is a diagram depicting a configuration example of therectification circuit in the present embodiment;

FIG. 10 is a sectional view depicting a configuration of a MOStransistor as a limiter circuit in the present embodiment; and

FIG. 11 is a view for describing characteristics of the diodes and thelimiter circuits in the rectification circuit in the present embodiment.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments will be described based on the drawings.

FIG. 1 is a diagram depicting a configuration example of an RFID systemin a present embodiment. The RFID system in the present embodimentincludes a reader/writer 10 and an RFID tag 20 as a semiconductor devicein the present embodiment. The reader/writer 10 and the RFID tag 20wirelessly communicate with each other by transmitting and receivingradio frequency (RF) carrier signals (wireless signals) 30.

The reader/writer 10 includes a carrier generation circuit 11, a commandgeneration circuit 12, a modulation circuit 13, an antenna 14, and areception circuit 15. For example, the carrier generation circuit 11 isan oscillator. The carrier generation circuit 11 generates RF carriersignals. The command generation circuit 12 generates command signalseach containing a command or data to be transmitted to the RFID tag 20side. The command may be a command for reading information (e.g. ID)written in an RFID tag and a command for writing data in a specifiedaddress area in an RFID tag, for example.

The modulation circuit 13 modulates RF carrier signals generated by thecarrier generation circuit 11 corresponding to a command signal from thecommand generation circuit 12. The modulation system is amplitude shiftkeying (ASK) modulation indicating data “1” when a carrier is presentand data “0” when a carrier is not present, for example. The antenna 14transmits and receives RF carrier signals. The antenna 14 transmits RFcarrier signals modulated by the modulation circuit 13, and receives RFcarrier signals from the RFID tag 20 and supplies the carrier signals tothe reception circuit 15.

The reception circuit 15 receives response signals from the RFID tag 20via the antenna 14. The reception circuit 15 decodes received signalsand performs a process corresponding to response data. Because directinput of RF carrier signals from the modulation circuit 13 to thereception circuit 15 disturbs response signals from the RFID tag 20, acirculator, which is not depicted, etc. is inserted between themodulation circuit 13 and the reception circuit 15 and between themodulation circuit 13 and the antenna 14, for example, to preventleakage of signals.

The RFID tag 20 includes an antenna 21, a rectification circuit 22, areception circuit 23, a modulation circuit 24, a processing circuit 25,and a memory 26. The antenna 21 transmits and receives RF carriersignals. Modulated RF carrier signals (carrier signals modulatedcorresponding to commands) received from the reader/writer 10 by theantenna 21 are incident to the rectification circuit 22, the receptioncircuit 23, and the modulation circuit 24. The rectification circuit 22rectifies RF carrier signals received by the antenna 21 to generatepower supply voltage (DC voltage). Each of the circuits included in theRFID tag 20 is driven by the power supply voltage (DC voltage) generatedby the rectification circuit 22.

The reception circuit 23 extracts a command from a modulated RF carriersignal received by the antenna 21. A carrier signal in UHF band, forexample, has a frequency of 860 MHz to 960 MHz and a command bit rate of40 Kb/s to 160 Kb/s. Thus, the command can be extracted from a signalreceived by a low pass filter having a low-pass frequency band of about200 KHz.

The processing circuit 25 recognizes received commands at self-timing,and performs processes corresponding to the commands. The length of data“0”, the length of data “0” and data “1”, and the like precede a commandas a header and are transmitted from the reader/writer 10. Thus, Theprocessing circuit 25 performs the process based on the lengths. Thememory 26 is a readable and writable nonvolatile memory and retainsinformation (ID, production serial number, individual data, etc.) of theRFID tag 20. For example, the processing circuit 25 reads and writesinformation by accessing to the memory 26 based on content of a commandfrom the reader/writer 10 that the processing circuit 25 has recognized.

The modulation circuit 24 responses to the reader/writer 10 based on theresult of the process performed by the processing circuit 25corresponding to a command. The modulation circuit 24 generates a binarysignal consisting of “0” and “1” by absorbing or reflecting (impedancemodulation) an incident RF carrier signal unlike the modulation circuit13 of the reader/writer 10. For example, a transistor may be providedbetween the antenna 21 and a node supplied the reference potential, andthe modulation circuit 24 controls reflection amount through on-offcontrol of the transistor.

FIG. 2 is a diagram depicting a configuration example of a rectificationcircuit (multiplied voltage rectification circuit). A capacitor C1 hasone electrode connected to an input terminal receiving an input voltageVin and the other electrode connected to a cathode of a diode D1. Ananode of the diode D1 is connected to the reference potential linehaving a reference potential VSS. A capacitor C2 has one electrodeconnected to the reference potential line and the other electrodeconnected to a cathode of a diode D2 and an output terminal supplying anoutput voltage Vout. An anode of the diode D2 is connected to aninterconnection point between the other electrode of the capacitor C1and the cathode of the diode D1.

Rectifying operation of the rectification circuit depicted in FIG. 2will be described. It is assumed hereinafter that the input terminalreceives sine wave signal having amplitude of the potentials ±Vin withrespect to the reference potential VSS, and the on-voltages of thediodes D1 and D2 are both Von. When the potential of the input terminalis lower than the reference potential VSS and the difference between thepotential of the input terminal and the reference potential VSS is lowerthan the on-voltage Von of the diodes, current flows from the referencepotential line to the input terminal through the diode D1 and thecapacitor C1 to charge the capacitor C1. When the potential of the inputterminal is higher than the reference potential VSS and the differencebetween the potential of the input terminal and the reference potentialVSS is higher than the on-voltage Von of the diodes, current flows fromthe input terminal to the reference potential line through the capacitorC1, the diode D2, and the capacitor C2. At this time, the potential ofthe capacitor C1 charged in the previous step is added to the potentialof the input terminal, and to the resultant potential, the capacitor C2is charged. These steps are repeated so that the rectification circuitdepicted in FIG. 2 generates voltage {2×(Vin−Von)} as the output voltageVout.

The output voltage Vout of the rectification circuit (multiplied voltagerectification circuit) having the configuration depicted in FIG. 2 canbe expressed as Vout=N×(Vin−Von) using the input voltage Vin and theon-voltage Von of the diodes. In the expression, N is the number ofdiodes. The on-voltage Von of the diode may be 0.7 V for Si diode and0.2 to 0.3 V for schottky barrier diode (SBD), for example.

In the rectification circuit having the configuration depicted in FIG.2, circuits depicted in FIG. 2 may be stacked (in multistage connection)to increase the number of diodes or the on-voltage Von of the diodes maybe lowered in order to increase the output voltage Vout. FIG. 3 is adiagram depicting a configuration example of a rectification circuithaving twelve diodes by stacking (in multistage connection)rectification circuits having the circuit configuration depicted in FIG.2 as an example. FIG. 3 depicts an example where the configuration isapplied to the rectification circuit 22 of the RFID tag 20.

As surrounded by broken lines in FIG. 3, a set of capacitors C1 and C2and diodes D1 and D2, a set of capacitors C3 and C4 and diodes D3 andD4, a set of capacitors C5 and C6 and diodes D5 and D6, a set ofcapacitors C7 and C8 and diodes D7 and D8, a set of capacitors C9 andC10 and diodes D9 and D10, and a set of capacitors C11 and C12 anddiodes D11 and D12 each realize a rectification circuit (multipliedvoltage rectification circuit) similar to that depicted in FIG. 2.

An output node of the rectification circuit in the previous stage isconnected to the rectification circuit of the next stage to supply anoutput voltage of the rectification circuit of the previous stage to therectification circuit of the next stage. Specifically, an output node N3of a first rectification circuit including the capacitors C1 and C2 andthe diodes D1 and D2 is connected to a second rectification circuitincluding the capacitors C3 and C4 and the diodes D3 and D4. An outputnode N4 of the second rectification circuit is connected to a thirdrectification circuit including the capacitors C5 and C6 and the diodesD5 and D6. A potential of an output node of the third rectificationcircuit is output as a first output potential (a high potential of thegenerated power supply voltage) VDD.

In addition, an output node N2 of a fourth rectification circuitincluding the capacitors C7 and C8 and the diodes D7 and D8 is connectedto a fifth rectification circuit including the capacitors C9 and C10 anddiodes D9 and D10. An output node N1 of the fifth rectification circuitis connected to a sixth rectification circuit including the capacitorsC11 and C12 and the diodes D11 and D12. A potential of an output node ofthe sixth rectification circuit is output as a second output potential(a reference potential of the generated power supply voltage) VSS. Inthis embodiment, the output potential VSS is a substrate potential of asemiconductor integrated circuit (LSI), on which respective circuits inthe RFID tag 20 are formed, and the output voltage VDD, when the outputpotential VSS is the reference potential, is supplied to the respectivecircuits in the RFID tag 20.

In FIG. 3, antenna connection terminals PWRP and PWRM are depicted. Theantenna 21 is connected between the antenna connection terminals PWRPand PWRM. To the antenna 21, an RF carrier signal of a sine wave havingamplitude of a certain potential with respect to a potential of theterminal PWRM as depicted in FIG. 4 is input. FIG. 5 is a diagramdepicting change over time of potentials of respective nodes when thesignal depicted in FIG. 4 is applied between the terminals PWRP andPWRM. FIG. 5 depicts the potentials of respective nodes N1 to N4, VDD,and VSS with respect to the potential of the terminal PWRM as areference. In this embodiment, the RF carrier signal input between theterminals PWRP and PWRM is an RF carrier signal having beenASK-modulated by the reader/writer 10 though the RF carrier signal isnot depicted in FIG. 4.

FIG. 6 is a diagram depicting a layout example of the diodes in therectification circuit depicted in FIG. 3. Such linearly positioning ofthe diodes D1 to D12 of the rectification circuit of FIG. 3 in thelayout of FIG. 6 enables the rectification circuit to have a smallcircuit area. FIG. 7 is a sectional view taken along the line I-I inFIG. 6. In FIG. 7, a portion A includes the diode D12 and VSS, and aportion B includes the diode D6. P-type wells 72A, 72B, and 72C andN-type wells 73A and 73B are formed in a P-type substrate 71. Inaddition, Shallow Trench Isolation STI is depicted.

As depicted in FIG. 7, a cathode electrode 74B of the diode D12connected to the antenna connection terminal PWRP through the capacitorC11 is connected to the N-type well 73A through a contact. A schottkybarrier junction is formed between an anode electrode 74A of the diodeD12 and the N-type well 73A. A cathode electrode 75B of the diode D6connected to the output terminal having the output potential VDD isconnected to the N-type well 73B through a contact. A schottky barrierjunction is formed between an anode electrode 75A of the diode D6 andthe N-type well 73B. The P-type well 72B is brought to the potential VSSthrough wiring 76 and the like. In the configuration depicted in FIG. 7,there is present a parasitic NPN bipolar transistor constituted of theN-type well 73B included in the diode D6 (the portion B), the P-typewell 72B brought to the potential VSS, and the N-type well 73A includedin the diode D12 (the portion A).

In this embodiment, an antenna connection terminal is connected to adiode through a capacitor according to the configuration of arectification circuit (multiplied voltage rectification circuit). In theexample depicted in FIG. 3, the antenna connection terminal PWRP isconnected, for example, to a cathode of the diode D1 through thecapacitor C1, a cathode of the diode D3 through a capacitor C3, acathode of the diode D5 through a capacitor C5, a cathode of the diodeD8 through a capacitor C7, a cathode of the diode D10 through acapacitor C9, and a cathode of the diode D12 through a capacitor C11.Thus, increase of amplitude of a carrier signal received by the antennaupon short distance reception increases the peak voltage in positivedirection and negative direction with respect to the DC potentials ofthe cathodes of the diodes.

When the potential of the cathode electrode 74B of the diode D12connected to the antenna connection terminal PWRP through the capacitorC11 changes to the negative side because of large power input throughshort distance communication or the like, current flows from the P-typewell 72B of the potential VSS toward the N-type well 73A as the cathodeof the diode D12. The current flowing from the P-type well 72B towardthe N-type well 73A corresponds to base current. Current obtained bymultiplying the current by the current gain flows from the N-type well73B as the cathode of the diode D6 toward the N-type well 73A as thecathode of the diode D12. The current flowing from the N-type well 73Btoward the N-type well 73A corresponds to collector current.

Thus, the potential of the cathode of the diode D6, in other word, theoutput potential VDD is lowered, disabling normal power supply to othercircuits to prevent stable operation of the circuits, therebyinstability or impossibility of communication may be caused. In order tolower the collector current, the distance between circuits may beelongated to add wiring resistance so as to lower the base current.However, this unfortunately increases a circuit area.

Thus, in the present embodiment, limiter circuits are provided asdepicted in FIG. 8, and node potentials between the capacitors connectedto the antenna connection terminal PWRP and the cathodes of the diodesare limited by the limiter circuits so as to suppress change of the nodepotentials with respect to the potential VSS to the negative side. Thissuppresses increase of the base current of a parasitic bipolartransistor constituted of the diodes D6 and D12, and suppresses loweringof the output potential VDD.

FIG. 8 is a diagram depicting a configuration example of therectification circuit (multiplied voltage rectification circuit) in thepresent embodiment. FIG. 8 depicts an example where the limiter circuitsare provided for the rectification circuit having twelve diodes depictedin FIG. 3.

As described above, the set of the capacitors C1 and C2 and the diodesD1 and D2, the set of the capacitors C3 and C4 and the diodes D3 and D4,the set of the capacitors C5 and C6 and the diodes D5 and D6, the set ofthe capacitors C7 and C8 and the diodes D7 and D8, the set of thecapacitors C9 and C10 and the diodes D9 and D10, and the set of thecapacitors C11 and C12 and the diodes D11 and D12 each realize arectification circuit (multiplied voltage rectification circuit) similarto that depicted in FIG. 2.

An output node of the rectification circuit in the previous stage isconnected to the rectification circuit of the next stage to supply anoutput voltage of the rectification circuit of the previous stage to therectification circuit of the next stage. Specifically, the output nodeN3 of the first rectification circuit including the capacitors C1 and C2and the diodes D1 and D2 is connected to the second rectificationcircuit including the capacitors C3 and C4 and the diodes D3 and D4. Theoutput node N4 of the second rectification circuit is connected to thethird rectification circuit including the capacitors C5 and C6 and thediodes D5 and D6. The potential of the output node of the thirdrectification circuit is output as a first output potential (a highpotential of the generated power supply voltage) VDD.

In addition, the output node N2 of the fourth rectification circuitincluding the capacitors C7 and C8 and the diodes D7 and D8 is connectedto the fifth rectification circuit including the capacitors C9 and C10and diodes D9 and D10. The output node N1 of the fifth rectificationcircuit is connected to the sixth rectification circuit including thecapacitors C11 and C12 and the diodes D11 and D12. The potential of theoutput node of the sixth rectification circuit is output as the secondoutput potential (the reference potential of the generated power supplyvoltage) VSS.

Between the capacitor C11 connected to the antenna connection terminalPWRP and a node N11 having the potential VSS, a limiter circuit LIM1 andthe diode D12 are connected in parallel. Between the capacitor C9connected to the antenna connection terminal PWRP and the node N11having the potential VSS, a limiter circuit LIM2 and the diode D10 areconnected in parallel. Between the capacitor C7 connected to the antennaconnection terminal PWRP and the node N11 having the potential VSS, alimiter circuit LIM3 and the diode D8 are connected in parallel.

When potentials of nodes N12, N13, and N14 between the capacitors C11,C9, and C7 and the diodes D12, D10, and D8 change to negative potentialswith respect to the potential VSS, the limiter circuits LIM1, LIM2, andLIM3 prevent the potentials from being lowered to a potential turning onparasitic bipolar transistors constituted of the corresponding diodes.Specifically, when potentials of the nodes N12, N13, and N14 change tonegative potentials with respect to the potential VSS, the limitercircuits LIM1, LIM2, and LIM3 clip the potentials at a certain potentialto limit lowering of the potentials such that potential differencesbetween the potentials of the nodes N12, N13, and N14 and the potentialVSS do not reach the potential turning on the parasitic bipolartransistors.

The limiter circuits LIM1, LIM2, and LIM3 have circuit characteristic102 depicted in FIG. 11, for example. According to the circuitcharacteristic 102, the limiter circuits LIM1, LIM2, and LIM3 are turnedon at a voltage V2 equal to or lower than a voltage V3, which turns onthe parasitic bipolar transistors, and allow current, which is largeenough not to make the potential differences between the potentials ofthe nodes N12, N13, N14 and the potential VSS reach the voltage V3, toflow. In FIG. 11, circuit characteristic 101 is characteristic of thediodes D1 to D12. As depicted in FIG. 11, the diodes D1 to D12 areturned on at a voltage V1 lower than the voltage V2 turning on thelimiter circuits LIM1, LIM2, and LIM3. Thus, highly efficient rectifyingcharacteristic can be realized. Note that, as the diodes D1 to D12 ofthe rectification circuit, schottky barrier diodes (SBD) having a lowon-voltage, for example, may be used to realize highly efficientrectifying characteristic.

FIG. 9 is a diagram depicting a circuit configuration example of arectification circuit (multiplied voltage rectification circuit) in thepresent embodiment. FIG. 9 depicts an example, in which the limitercircuits LIM1, LIM2, and LIM3 depicted in FIG. 8 are realized bydiode-connected N-channel type MOS transistors T1, T2, and T3.

Between the node N11 having the potential VSS and the cathode of thediode D12 (the node N12), a diode-connected N-channel type MOStransistor T1 as a limiter circuit is connected. Between the node N11having the potential VSS and the cathode of the diode D10 (node N13), adiode-connected N-channel type MOS transistor T2 as a limiter circuit isconnected. Between the node N11 having the potential VSS and the cathodeof the diode D8 (node N14), a diode-connected N-channel type MOStransistor T3 as a limiter circuit is connected.

FIG. 10 is a sectional view depicting a configuration example of theN-channel type MOS transistors T1, T2, and T3. On a P-type substrate 91,an N-type well 92 is formed. In the N-type well 92, a P-type well 93 isformed. In the P-type well 93, N+ diffusion layers to be a source regionand a drain region are formed. On the N+ diffusion layers, a sourceelectrode 95 and a drain electrode 96 are respectively formed. On achannel region between the source region and the drain region, a gateelectrode 98 is formed through a gate insulating film (oxide film) 97.

Setting a threshold voltage of the N-channel type MOS transistors T1,T2, and T3 to Vth, and configuring the N-channel type MOS transistorsT1, T2, and T3 as depicted in FIG. 9 can keep the potentials of thenodes N12, N13, N14 higher than (Vss−Vth). Since the diode-connectedN-channel type MOS transistors T1, T2, and T3 are used as limitercircuits, a capacity of only one of the source and the drain is appliedas a load, which can suppress increase of load capacity caused byproviding limiter circuits.

According to the embodiment, between the capacitors, to which theantenna connection terminal PWRP is connected, and the nodes having thepotential VSS, diodes as rectifier elements having a low threshold valueand limiter circuits that have a high threshold and clamp the potentialsare connected in parallel. Thus, when the potentials of the cathodes ofthe diodes are negative potentials with respect to the potential VSS,the node potentials between capacitors, to which the antenna connectionterminal PWRP is connected, and the cathodes of the diodes are limitedby a limiter circuit such that the potential differences between thepotentials of the cathodes and the potential VSS are equal to or lowerthan the voltage turning on the parasitic bipolar transistors.Therefore, even when large power is input through short distancecommunication or the like, changing of the cathode potentials of thediodes to the negative potential side is suppressed, and lowering of theoutput potential VDD is also suppressed, thereby enabling stablecommunication even when an RFID tag is at a short distance with respectto the reader/writer. In addition, the use of rectifier elements havinga low threshold value can suppress lowering of the rectifyingcharacteristic.

The disclosed semiconductor device can suppress changing of cathodepotentials of the diodes of the rectification circuit to the negativepotential side even when a wireless signal having large power is input,and suppress lowering of the output voltage, thereby enabling stablecommunication even when the RFID tag is at a short distance with respectto the reader/writer.

While certain embodiments have been described, these embodiments of theinvention have been presented by way of example only, and the scope ofthe technical scope of the inventions should not be restrictivelyinterpreted based on the embodiments. Specifically, the invention hereinmay be embodied in a variety of forms without departing from thetechnical spirit and essential characteristic thereof.

All examples and conditional language provided herein are intended forthe pedagogical purposes of aiding the reader in understanding theinvention and the concepts contributed by the inventor to further theart, and are not to be construed as limitations to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although one or more embodiments of thepresent invention have been described in detail, it should be understoodthat the various changes, substitutions, and alterations could be madehereto without departing from the spirit and scope of the invention.

What is claimed is:
 1. A semiconductor device comprising: an antenna that transmits and receives a wireless signal; and a rectification circuit that includes unit rectification circuits connected in multistage and generates a power supply voltage from the wireless signal received by the antenna connected to the rectification circuit through an antenna connection terminal, each unit rectification circuit includes a plurality of capacitors and a plurality of diodes, wherein the rectification circuit includes limiter circuits that are turned on at a voltage larger than an on-voltage of the diodes, clamp cathodes of the diodes at a first voltage, and the limiter circuits and the diodes are connected in parallel between the capacitors connected to the antenna connection terminal and a node supplied a reference potential of the power supply voltage.
 2. The semiconductor device according to claim 1, wherein the limiter circuits are diode-connected MOS transistors connected between the capacitors connected to the antenna connection terminal and the node supplied reference potential of the power supply voltage.
 3. The semiconductor device according to claim 2, wherein the first voltage is smaller than a threshold voltage of a parasitic bipolar transistors constituted of the diodes of the rectification circuit.
 4. The semiconductor device according to claim 2, further comprising: a reception circuit that extracts a command from the wireless signal received by the antenna; a processing circuit that performs a process corresponding to the received command; a nonvolatile memory to be accessed by the processing circuit; and a modulation circuit that generates a response signal based on result of a process corresponding to the command, wherein the reception circuit, the processing circuit, the nonvolatile memory, and the modulation circuit are driven by the power supply voltage generated by the rectification circuit.
 5. The semiconductor device according to claim 3, wherein the diodes of the rectification circuit are schottky barrier diodes, and the limiter circuits are diode-connected MOS transistors.
 6. The semiconductor device according to claim 5, further comprising: a reception circuit that extracts a command from the wireless signal received by the antenna; a processing circuit that performs a process corresponding to the received command; a nonvolatile memory to be accessed by the processing circuit; and a modulation circuit that generates a response signal based on result of a process corresponding to the command, wherein the reception circuit, the processing circuit, the nonvolatile memory, and the modulation circuit are driven by the power supply voltage generated by the rectification circuit.
 7. The semiconductor device according to claim 1, wherein the first voltage is smaller than a threshold voltage of a parasitic bipolar transistors constituted of the diodes of the rectification circuit.
 8. The semiconductor device according to claim 7, further comprising: a reception circuit that extracts a command from the wireless signal received by the antenna; a processing circuit that performs a process corresponding to the received command; a nonvolatile memory to be accessed by the processing circuit; and a modulation circuit that generates a response signal based on result of a process corresponding to the command, wherein the reception circuit, the processing circuit, the nonvolatile memory, and the modulation circuit are driven by the power supply voltage generated by the rectification circuit.
 9. The semiconductor device according to claim 1, further comprising: a reception circuit that extracts a command from the wireless signal received by the antenna; a processing circuit that performs a process corresponding to the received command; a nonvolatile memory to be accessed by the processing circuit; and a modulation circuit that generates a response signal based on result of a process corresponding to the command, wherein the reception circuit, the processing circuit, the nonvolatile memory, and the modulation circuit are driven by the power supply voltage generated by the rectification circuit. 